摘要: We describe monocrystalline graphitic films, which are a
few atoms thick but are nonetheless stable under ambient conditions, metallic,
and of remarkably high quality. The films are found to be a two-dimensional
semimetal with a tiny overlap between valence and conductance bands, and they
exhibit a strong ambipolar electric field effect such that electrons and holes
in concentrations up to 10(13) per square centimeter and with room-temperature
mobilities of similar to10,000 square centimeters per volt-second can be induced
by applying gate voltage.

摘要: Fullerene single-wall nanotubes (SWNTs) were produced in
yields of more than 70 percent by condensation of a laser-vaporized
carbon-nickel-cobalt mixture at 1200 degrees C. X-ray diffraction and electron
microscopy showed that these SWNTs are nearly uniform. in diameter and thai they
self-organize into ''ropes,'' which consist of 100 to 500 SWNTs in a
two-dimensional triangular lattice with a lattice constant of 17 angstroms. The
x-ray form. factor is consistent with that of uniformly charged cylinders 13.8
+/- 0.2 angstroms in diameter. The ropes were metallic, with a single-rope
resistivity of <10(-4) ohm-centimeters at 300 kelvin. The uniformity of SWNT
diameter is attributed to the efficient annealing of an initial fullerene
tubelet kept open by a few metal atoms; the optimum diameter is determined by
competition between the strain energy of curvature of the graphene sheet and the
dangling-bond energy of the open edge, where growth occurs. These factors
strongly favor the metallic (10,10) tube with C-5v symmetry and an open edge
stabilized by triple bonds.

摘要: Quantum electrodynamics ( resulting from the merger of
quantum mechanics and relativity theory) has provided a clear understanding of
phenomena ranging from particle physics to cosmology and from astrophysics to
quantum chemistry(1-3). The ideas underlying quantum electrodynamics also
influence the theory of condensed matter(4,5), but quantum relativistic effects
are usually minute in the known experimental systems that can be described
accurately by the non-relativistic Schrodinger equation. Here we report an
experimental study of a condensed-matter system (graphene, a single atomic layer
of carbon(6,7)) in which electron transport is essentially governed by Dirac's (
relativistic) equation. The charge carriers in graphene mimic relativistic
particles with zero rest mass and have an effective 'speed of light' c*
approximate to 10(6) m s(-1). Our study reveals a variety of unusual phenomena
that are characteristic of two-dimensional Dirac fermions. In particular we have
observed the following: first, graphene's conductivity never falls below a
minimum value corresponding to the quantum unit of conductance, even when
concentrations of charge carriers tend to zero; second, the integer quantum Hall
effect in graphene is anomalous in that it occurs at half-integer filling
factors; and third, the cyclotron mass m(c) of massless carriers in graphene is
described by E = m(c)c(*)(2). This two-dimensional system is not only
interesting in itself but also allows access to the subtle and rich physics of
quantum electrodynamics in a bench-top experiment.

ISSN: 0028-0836

DOI: 10.1038/nature04233

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作者: Geim, AK (Geim, A. K.); Novoselov, KS (Novoselov, K.
S.)

标题: The rise of graphene

来源出版物: NATURE MATERIALS, 6 (3): 183-191 MAR 2007

摘要: Graphene is a rapidly rising star on the horizon of
materials science and condensed-matter physics. This strictly two-dimensional
material exhibits exceptionally high crystal and electronic quality, and,
despite its short history, has already revealed a cornucopia of new physics and
potential applications, which are briefly discussed here. Whereas one can be
certain of the realness of applications only when commercial products appear,
graphene no longer requires any further proof of its importance in terms of
fundamental physics. Owing to its unusual electronic spectrum, graphene has led
to the emergence of a new paradigm of 'relativistic' condensed-matter physics,
where quantum relativistic phenomena, some of which are unobservable in
high-energy physics, can now be mimicked and tested in table-top experiments.
More generally, graphene represents a conceptually new class of materials that
are only one atom thick, and, on this basis, offers new inroads into
low-dimensional physics that has never ceased to surprise and continues to
provide a fertile ground for applications.

ISSN: 1476-1122

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作者: Zhang, YB; Tan, YW; Stormer, HL; Kim, P

标题: Experimental observation of the quantum Hall effect and
Berry's phase in graphene

来源出版物: NATURE, 438 (7065): 201-204 NOV 10 2005

摘要: When electrons are confined in two-dimensional materials,
quantum-mechanically enhanced transport phenomena such as the quantum Hall
effect can be observed. Graphene, consisting of an isolated single atomic layer
of graphite, is an ideal realization of such a two-dimensional system. However,
its behaviour is expected to differ markedly from the well-studied case of
quantum wells in conventional semiconductor interfaces. This difference arises
from the unique electronic properties of graphene, which exhibits electron -
hole degeneracy and vanishing carrier mass near the point of charge
neutrality(1,2). Indeed, a distinctive half-integer quantum Hall effect has been
predicted(3-5) theoretically, as has the existence of a non-zero Berry's phase (
a geometric quantum phase) of the electron wavefunction - a consequence of the
exceptional topology of the graphene band structure(6,7). Recent advances in
micromechanical extraction and fabrication techniques for graphite
structures(8-12) now permit such exotic two-dimensional electron systems to be
probed experimentally. Here we report an experimental investigation of
magneto-transport in a high-mobility single layer of graphene. Adjusting the
chemical potential with the use of the electric field effect, we observe an
unusual half-integer quantum Hall effect for both electron and hole carriers in
graphene. The relevance of Berry's phase to these experiments is confirmed by
magneto-oscillations. In addition to their purely scientific interest, these
unusual quantum transport phenomena may lead to new applications in carbon-based
electronic and magneto-electronic devices.

ISSN: 0028-0836

DOI: 10.1038/nature04235

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作者: Hu, JT; Odom, TW; Lieber, CM

标题: Chemistry and physics in one dimension: Synthesis and
properties of nanowires and nanotubes

来源出版物: ACCOUNTS OF CHEMICAL RESEARCH, 32 (5): 435-445 MAY
1999

ISSN: 0001-4842

显示 7 条，共 50 条

作者: SAITO, R; FUJITA, M; DRESSELHAUS, G; DRESSELHAUS,
MS

标题: ELECTRONIC-STRUCTURE OF CHIRAL GRAPHENE TUBULES

来源出版物: APPLIED PHYSICS LETTERS, 60 (18): 2204-2206 MAY 4
1992

摘要: The electronic structure for graphene monolayer tubules is
predicted as a function of the diameter and helicity of the constituent graphene
tubules. The calculated results show that approximately 1/3 of these tubules are
a one-dimensional metal which is stable against a Peierls distortion, and the
other 2/3 are one-dimensional semiconductors. The implications of these results
are discussed.

摘要: Single wall carbon nanotubes (SWNTs) that are found as
close-packed arrays in crystalline ropes have been studied by using Raman
scattering techniques with laser excitation wavelengths in the range from 514.5
to 1320 nanometers. Numerous Raman peaks were observed and identified with
vibrational modes of armchair symmetry (n, n) SWNTs. The Raman spectra are in
good agreement with lattice dynamics calculations based on C-C force constants
used to fit the two-dimensional, experimental phonon dispersion of a single
graphene sheet. Calculated intensities from a nonresonant, bond polarizability
model optimized for sp(2) carbon are also in qualitative agreement with the
Raman data, although a resonant Raman scattering process is also taking place.
This resonance results from the one-dimensional quantum confinement of the
electrons in the nanotube.

摘要: Carbon nanotubes(1) are predicted to be metallic or
semiconducting depending on their diameter and the helicity of the arrangement
of graphitic rings in their walls(2-5). Scanning tunnelling microscopy (STM)
offers the potential to probe this prediction, as it can resolve simultaneously
both atomic structure and the electronic density of states. Previous STM studies
of multi-walled nanotubes(6-9) and single-walled nanotubes (SWNTs)(10) have
provided indications of differing structures and diameter-dependent electronic
properties, but have not revealed any explicit relationship between structure
and electronic properties, Here we report STM measurements of the atomic
structure and electronic properties of SWNTs. We are able to resolve the
hexagonal-ring structure of the walls, and show that the electronic properties
do indeed depend on diameter and helicity. We find that the SWNT samples exhibit
many different structures, with no one species dominating.

摘要: This article reviews the basic theoretical aspects of
graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional
Dirac-like electronic excitations. The Dirac electrons can be controlled by
application of external electric and magnetic fields, or by altering sample
geometry and/or topology. The Dirac electrons behave in unusual ways in
tunneling, confinement, and the integer quantum Hall effect. The electronic
properties of graphene stacks are discussed and vary with stacking order and
number of layers. Edge (surface) states in graphene depend on the edge
termination (zigzag or armchair) and affect the physical properties of
nanoribbons. Different types of disorder modify the Dirac equation leading to
unusual spectroscopic and transport properties. The effects of electron-electron
and electron-phonon interactions in single layer and multilayer graphene are
also presented.

摘要: Ultrathin epitaxial graphite was grown on single-crystal
silicon carbide by vacuum graphitization. The material can be patterned using
standard nanolithography methods. The transport properties, which are closely
related to those of carbon nanotubes, are dominated by the single epitaxial
graphene layer at the silicon carbide interface and reveal the Dirac nature of
the charge carriers. Patterned structures show quantum confinement of electrons
and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities
exceeding 2.5 square meters per volt-second. All-graphene electronically
coherent devices and device architectures are envisaged.

摘要: Field emission of electrons from individually mounted
carbon nanotubes has been found to be dramatically enhanced when the nanotube
tips are opened by laser evaporation or oxidative etching. Emission currents of
0.1 to 1 microampere were readily obtained at room temperature with bias
voltages of less than 80 volts, The emitting structures are concluded to be
linear chains of carbon atoms, C-n (n = 10 to 100), pulled out from the open
edges of the graphene wall layers of the nanotube by the force of the electric
field, in a process that resembles unraveling the sleeve of a
sweater.

摘要: Carbon nanotubes display either metallic or semiconducting
properties. Both Large, multiwalled nanotubes (MWNTs), with many concentric
carbon shells, and bundles or "ropes" of aligned single-walled nanotubes
(SWNTs), are complex composite conductors that incorporate many weakly coupled
nanotubes that each have a different electronic structure. Here we demonstrate a
simple and reliable method for selectively removing single carbon shells from
MWNTs and SWNT ropes to tailor the properties of these composite nanotubes. We
can remove shells of MWNTs stepwise and individually characterize the different
shells. By choosing among the shells, we can convert a MWNT into either a
metallic or a semiconducting conductor, as well as directly address the issue of
multiple-shell transport. With SWNT ropes, similar selectivity allows us to
generate entire arrays of nanoscale field-effect transistors based solely on the
fraction of semiconducting SWNTs.

摘要: Graphene sheets - one- atom-thick two-dimensional layers
of sp(2)-bonded carbon - are predicted to have a range of unusual properties.
Their thermal conductivity and mechanical stiffness may rival the remarkable
in-plane values for graphite (similar to 3,000 W m(-1) K-1 and 1,060 GPa,
respectively); their fracture strength should be comparable to that of carbon
nanotubes for similar types of defects(1-3); and recent studies have shown that
individual graphene sheets have extraordinary electronic transport
properties(4-8). One possible route to harnessing these properties for
applications would be to incorporate graphene sheets in a composite material.
The manufacturing of such composites requires not only that graphene sheets be
produced on a sufficient scale but that they also be incorporated, and
homogeneously distributed, into various matrices. Graphite, inexpensive and
available in large quantity, unfortunately does not readily exfoliate to yield
individual graphene sheets. Here we present a general approach for the
preparation of graphene-polymer composites via complete exfoliation of
graphite(9) and molecular-level dispersion of individual, chemically modified
graphene sheets within polymer hosts. A polystyrene - graphene composite formed
by this route exhibits a percolation threshold(10) of similar to 0.1 volume per
cent for room-temperature electrical conductivity, the lowest reported value for
any carbon-based composite except for those involving carbon nanotubes(11); at
only 1 volume per cent, this composite has a conductivity of similar to 0.1 S
m(-1), sufficient for many electrical applications(12). Our bottom-up chemical
approach of tuning the graphene sheet properties provides a path to a broad new
class of graphene-based materials and their use in a variety of
applications.

摘要: Finite graphite systems having a zigzag edge exhibit a
special edge state. The corresponding energy bands are almost flat at the Fermi
level and thereby give a sharp peak in the density of states. The charge density
in the edge state is strongly localized on the zigzag edge sites. No such
localized state appears in graphite systems having an armchair edge. By
utilizing the graphene ribbon model, we discuss the effect of the system size
and edge shape on the special edge state. By varying the width of the graphene
ribbons, we find that the nanometer size effect is crucial for determining the
relative importance of the edge state. We also have extended the graphene ribbon
to have edges of a general shape, which is defined as a mixture of zigzag and
armchair sites. Examining the relative importance of the edge state for graphene
ribbons with general edges, we find that a non-negligible edge state survives
even in graphene ribbons with less developed zigzag edges. We demonstrate that
such an edge shape with three or four zigzag sites per sequence is sufficient to
show an edge state, when the system size is on a nanometer scale. The special
characteristics of the edge state play a large role in determining the density
of states near the Fermi level for graphite networks on a nanometer
scale.

来源出版物: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE
UNITED STATES OF AMERICA, 102 (30): 10451-10453 JUL 26 2005

摘要: We report free-standing atomic crystals that are strictly
2D and can be viewed as individual atomic planes pulled out of bulk crystals or
as unrolled single-wall nanotubes. By using micromechanical cleavage, we have
prepared and studied a variety of 2D crystals including single layers of boron
nitride, graphite, several dichalcogenicles, and complex oxides. These
atomically thin sheets (essentially gigantic 2D molecules unprotected from the
immediate environment) are stable under ambient conditions, exhibit high crystal
quality, and are continuous on a macroscopic scale.

ISSN: 0027-8424

DOI: 10.1073/pnas.0502848102

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作者: SAITO, R; FUJITA, M; DRESSELHAUS, G; DRESSELHAUS,
MS

标题: ELECTRONIC-STRUCTURE OF GRAPHENE TUBULES BASED ON
C-60

来源出版物: PHYSICAL REVIEW B, 46 (3): 1804-1811 JUL 15
1992

摘要: The electronic structures of some possible carbon fibers
nucleated from the hemisphere of a C60 molecule are presented. A one-dimensional
electronic band-structure model of such carbon fibers, having not only
rotational symmetry but also screw axes, is derived by folding the
two-dimensional energy bands of graphite. A simple tight-binding model shows
that some fibers are metallic and are stable against perturbations of the
one-dimensional energy bands and the mixing of sigma and pi-bands due to the
curvature of the circumference of the fiber.

ISSN: 0163-1829

显示 18 条，共 50 条

作者: Berber, S; Kwon, YK; Tomanek, D

标题: Unusually high thermal conductivity of carbon
nanotubes

来源出版物: PHYSICAL REVIEW LETTERS, 84 (20): 4613-4616 MAY 15
2000

摘要: Combining equilibrium and nonequilibrium molecular
dynamics simulations with accurate carbon potentials, we determine the thermal
conductivity lambda of carbon nanotubes and its dependence on temperature. Our
results suggest an unusually high value, lambda approximate to 6600 W/m K, for
an isolated (10, 10) nanotube at room temperature, comparable to the thermal
conductivity of a hypothetical isolated graphene monolayer or diamond. Our
results suggest that these high values of lambda are associated with the large
phonon mean free paths in these systems; substantially lower values are
predicted and observed for the basal plane of bulk graphite.

摘要: We investigate electronic transport in lithographically
patterned graphene ribbon structures where the lateral confinement of charge
carriers creates an energy gap near the charge neutrality point. Individual
graphene layers are contacted with metal electrodes and patterned into ribbons
of varying widths and different crystallographic orientations. The temperature
dependent conductance measurements show larger energy gaps opening for narrower
ribbons. The sizes of these energy gaps are investigated by measuring the
conductance in the nonlinear response regime at low temperatures. We find that
the energy gap scales inversely with the ribbon width, thus demonstrating the
ability to engineer the band gap of graphene nanostructures by lithographic
processes.

摘要: Graphene is the two-dimensional building block for carbon
allotropes of every other dimensionality. We show that its electronic structure
is captured in its Raman spectrum that clearly evolves with the number of
layers. The D peak second order changes in shape, width, and position for an
increasing number of layers, reflecting the change in the electron bands via a
double resonant Raman process. The G peak slightly down-shifts. This allows
unambiguous, high-throughput, nondestructive identification of graphene layers,
which is critically lacking in this emerging research area.

ISSN: 0031-9007

文献编号: 187401

DOI: 10.1103/PhysRevLett.97.187401

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作者: Dresselhaus, MS; Eklund, PC

标题: Phonons in carbon nanotubes

来源出版物: ADVANCES IN PHYSICS, 49 (6): 705-814 SEP
2000

摘要: A broad review of the unusual one-dimensional properties
of phonons in carbon nanotubes is presented, including phonons in isolated
nanotubes and in crystalline arrays of nanotubes in nanotube bundles. The main
technique for probing the phonon spectra has been Raman spectroscopy and the
many unique and unusual features of the Raman spectra of carbon nanotubes are
reviewed. Also included is a brief review of the thermal properties of carbon
nanotubes in relation to their unusual phonon dispersion relations and density
of states.

摘要: We have produced ultrathin epitaxial graphite films which
show remarkable 2D electron gas (2DEG) behavior. The films, composed of
typically three graphene sheets, were grown by thermal decomposition on the
(0001) surface of 6H-SiC, and characterized by surface science techniques. The
low-temperature conductance spans a range of localization regimes according to
the structural state (square resistance 1.5 kOmega to 225 kOmega at 4 K, with
positive magnetoconductance). Low-resistance samples show characteristics of
weak localization in two dimensions, from which we estimate elastic and
inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5
T, which is well-explained by n-type carriers of density 10(12) cm(-2) per
graphene sheet. The most highly ordered sample exhibits Shubnikov-de Haas
oscillations that correspond to nonlinearities observed in the Hall resistance,
indicating a potential new quantum Hall system. We show that the high-mobility
films can be patterned via conventional lithographic techniques, and we
demonstrate modulation of the film conductance using a top-gate electrode. These
key elements suggest electronic device applications based on nanopatterned
epitaxial graphene (NPEG), with the potential for large-scale
integration.

摘要: Electrical current can be completely spin polarized in a
class of materials known as half- metals, as a result of the coexistence of
metallic nature for electrons with one spin orientation and insulating nature
for electrons with the other. Such asymmetric electronic states for the
different spins have been predicted for some ferromagnetic metals - for example,
the Heusler compounds(1) and were first observed in a manganese perovskite (2).
In view of the potential for use of this property in realizing spin- based
electronics, substantial efforts have been made to search for half-metallic
materials(3,4). However, organic materials have hardly been investigated in this
context even though carbon- based nanostructures hold significant promise for
future electronic devices (5). Here we predict half- metallicity in nanometre-
scale graphene ribbons by using first- principles calculations. We show that
this phenomenon is realizable if in- plane homogeneous electric fields are
applied across the zigzag- shaped edges of the graphene nanoribbons, and that
their magnetic properties can be controlled by the external electric fields. The
results are not only of scientific interest in the interplay between electric
fields and electronic spin degree of freedom in solids 6,7 but may also open a
new path to explore spintronics(3) at the nanometre scale, based on graphene(8 -
11).

摘要: Based on a first-principles approach, we present scaling
rules for the band gaps of graphene nanoribbons (GNRs) as a function of their
widths. The GNRs considered have either armchair or zigzag shaped edges on both
sides with hydrogen passivation. Both varieties of ribbons are shown to have
band gaps. This differs from the results of simple tight-binding calculations or
solutions of the Dirac's equation based on them. Our ab initio calculations show
that the origin of energy gaps for GNRs with armchair shaped edges arises from
both quantum confinement and the crucial effect of the edges. For GNRs with
zigzag shaped edges, gaps appear because of a staggered sublattice potential on
the hexagonal lattice due to edge magnetization. The rich gap structure for
ribbons with armchair shaped edges is further obtained analytically including
edge effects. These results reproduce our ab initio calculation results very
well.

摘要: We developed a chemical route to produce graphene
nanoribbons ( GNR) with width below 10 nanometers, as well as single ribbons
with varying widths along their lengths or containing lattice- defined graphene
junctions for potential molecular electronics. The GNRs were solution-phase -
derived, stably suspended in solvents with noncovalent polymer
functionalization, and exhibited ultrasmooth edges with possibly well- defined
zigzag or armchair- edge structures. Electrical transport experiments showed
that, unlike single- walled carbon nanotubes, all of the sub - 10- nanometer
GNRs produced were semiconductors and afforded graphene field effect transistors
with on- off ratios of about 10(7) at room temperature.

ISSN: 0036-8075

DOI: 10.1126/science.1150878

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作者: BLASE, X; BENEDICT, LX; SHIRLEY, EL; LOUIE, SG

标题: HYBRIDIZATION EFFECTS AND METALLICITY IN SMALL RADIUS
CARBON NANOTUBES

来源出版物: PHYSICAL REVIEW LETTERS, 72 (12): 1878-1881 MAR 21
1994

摘要: Hybridization of the sigma* and pi* states of the graphene
network is shown to be as important as band-folding effects in determining the
metallicity of small radius carbon nanotubes. Using detailed plane-wave ab
initio pseudopotential local density functional (LDA) calculations, we find that
the electronic properties of small tubes are significantly altered from those
obtained in previous tight-binding calculations. Strongly modified low-lying
conduction band states are introduced into the band gap of insulating tubes
because of strong sigma*-pi* hybridization. As a result, the LDA gaps of some
tubes are lowered by more than 50%, and a tube previously predicted to be
semiconducting is shown to be metallic.

摘要: The use of Raman spectroscopy to reveal the remarkable
structure and the unusual electronic and phonon properties of single wall carbon
nanotubes (SWNTs) is reviewed comprehensively. The various types of Raman
scattering processes relevant to carbon nanotubes are reviewed, and the
theoretical foundations for these topics are presented. ne most common
experimental techniques used to probe carbon nanotubes are summarized, followed
by a review of the novel experimental findings for each of the features in the
first order and second order Raman spectra for single wall carbon nanotubes.
These results are presented and discussed in connection with theoretical
considerations. Raman spectra for bundles of SWNTs, for SWNTs surrounded by
various common wrapping agents, and for isolated SWNTs at the single nanotube
level are reviewed. Some of the current research challenges facing the field are
briefly summarized. (c) 2004 Elsevier B.V. All rights reserved.

摘要: The so-called Klein paradox - unimpeded penetration of
relativistic particles through high and wide potential barriers - is one of the
most exotic and counterintuitive consequences of quantum electrodynamics. The
phenomenon is discussed in many contexts in particle, nuclear and astro-physics
but direct tests of the Klein paradox using elementary particles have so far
proved impossible. Here we show that the effect can be tested in a conceptually
simple condensed-matter experiment using electrostatic barriers in single- and
bi-layer graphene. Owing to the chiral nature of their quasiparticles, quantum
tunnelling in these materials becomes highly anisotropic, qualitatively
different from the case of normal, non-relativistic electrons. Massless Dirac
fermions in graphene allow a close realization of Klein's gedanken experiment,
whereas massive chiral fermions in bilayer graphene offer an interesting
complementary system that elucidates the basic physics involved.

ISSN: 1745-2473

DOI: 10.1038/nphys384

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作者: Hernandez, E; Goze, C; Bernier, P; Rubio, A

标题: Elastic properties of C and BxCyNz composite
nanotubes

来源出版物: PHYSICAL REVIEW LETTERS, 80 (20): 4502-4505 MAY 18
1998

摘要: We present a comparative study of the energetic,
structural, and elastic properties of carbon and composite single-wall
nanotubes, including BN, BC3, and BC2N nanotubes, using a nonorthogonal
tight-binding formalism. Our calculations predict that carbon nanotubes have a
higher Young modulus than any of the studied composite nanotubes, and of the
same order as that found for defect-free graphene sheets. We obtain good
agreement with the available experimental results.

摘要: The ultimate aim of any detection method is to achieve
such a level of sensitivity that individual quanta of a measured entity can be
resolved. In the case of chemical sensors, the quantum is one atom or molecule.
Such resolution has so far been beyond the reach of any detection technique,
including solid-state gas sensors hailed for their exceptional sensitivity(1-4).
The fundamental reason limiting the resolution of such sensors is fluctuations
due to thermal motion of charges and defects(5), which lead to intrinsic noise
exceeding the sought-after signal from individual molecules, usually by many
orders of magnitude. Here, we show that micrometre-size sensors made from
graphene are capable of detecting individual events when a gas molecule attaches
to or detaches from graphene's surface. The adsorbed molecules change the local
carrier concentration in graphene one by one electron, which leads to step-like
changes in resistance. The achieved sensitivity is due to the fact that graphene
is an exceptionally low-noise material electronically, which makes it a
promising candidate not only for chemical detectors but also for other
applications where local probes sensitive to external charge, magnetic field or
mechanical strain are required.

摘要: We describe the synthesis of bilayer graphene thin films
deposited on insulating silicon carbide and report the characterization of their
electronic band structure using angle-resolved photoemission. By selectively
adjusting the carrier concentration in each layer, changes in the Coulomb
potential led to control of the gap between valence and conduction bands. This
control over the band structure suggests the potential application of bilayer
graphene to switching functions in atomic-scale electronic devices.

摘要: Single-walled carbon nanotubes(1) (SWNTs) are predicted to
be metallic for certain diameters and pitches of the twisted graphene ribbons
that make up their walls(2). Chemical doping is expected to substantially
increase the density of free charge carriers and thereby enhance the electrical
(and thermal) conductivity. Here we use Raman spectroscopy to study the effects
of exposing SWNT bundles(1) to typical electron-donor (potassium, rubidium) and
electron-acceptor (iodine, bromine) dopants. We find that the high-frequency
tangential vibrational modes of the carbon atoms in the SWNTs shift
substantially to lower (for K, Rb) or higher (for Br-2) frequencies. Little
change is seen for I-2 doping. These shifts provide evidence for charge transfer
between the dopants and the nanotubes, indicating an ionic character of the
doped samples. This, together with conductivity measurements(3), suggests that
doping does increase the carrier concentration of the SWNT bundles.

ISSN: 0028-0836

显示 33 条，共 50 条

作者: Peres, NMR; Guinea, F; Neto, AHC

标题: Electronic properties of disordered two-dimensional
carbon

来源出版物: PHYSICAL REVIEW B, 73 (12): Art. No. 125411 MAR
2006

摘要: Two-dimensional carbon, or graphene, is a semimetal that
presents unusual low-energy electronic excitations described in terms of Dirac
fermions. We analyze in a self-consistent way the effects of localized
(impurities or vacancies) and extended (edges or grain boundaries) defects on
the electronic and transport properties of graphene. On the one hand, point
defects induce a finite elastic lifetime at low energies with the enhancement of
the electronic density of states close to the Fermi level. Localized disorder
leads to a universal, disorder independent, electrical conductivity at low
temperatures, of the order of the quantum of conductance. The static
conductivity increases with temperature and shows oscillations in the presence
of a magnetic field. The graphene magnetic susceptibility is temperature
dependent (unlike an ordinary metal) and also increases with the amount of
defects. Optical transport properties are also calculated in detail. On the
other hand, extended defects induce localized states near the Fermi level. In
the absence of electron-hole symmetry, these states lead to a transfer of charge
between the defects and the bulk, the phenomenon we call self-doping. The role
of electron-electron interactions in controlling self-doping is also analyzed.
We also discuss the integer and fractional quantum Hall effect in graphene, the
role played by the edge states induced by a magnetic field, and their relation
to the almost field independent surface states induced at boundaries. The
possibility of magnetism in graphene, in the presence of short-range
electron-electron interactions and disorder is also analyzed.

摘要: The recent discovery of graphene has sparked much
interest, thus far focused on the peculiar electronic structure of this
material, in which charge carriers mimic massless relativistic particles(1-3).
However, the physical structure of graphene - a single layer of carbon atoms
densely packed in a honeycomb crystal lattice - is also puzzling. On the one
hand, graphene appears to be a strictly two-dimensional material, exhibiting
such a high crystal quality that electrons can travel submicrometre distances
without scattering. On the other hand, perfect two-dimensional crystals cannot
exist in the free state, according to both theory and experiment(4-9). This
incompatibility can be avoided by arguing that all the graphene structures
studied so far were an integral part of larger three-dimensional structures,
either supported by a bulk substrate or embedded in a three-dimensional
matrix(1-3,9-12). Here we report on individual graphene sheets freely suspended
on a microfabricated scaffold in vacuum or air. These membranes are only one
atom thick, yet they still display long-range crystalline order. However, our
studies by transmission electron microscopy also reveal that these suspended
graphene sheets are not perfectly flat: they exhibit intrinsic microscopic
roughening such that the surface normal varies by several degrees and
out-of-plane deformations reach 1 nm. The atomically thin single-crystal
membranes offer ample scope for fundamental research and new technologies,
whereas the observed corrugations in the third dimension may provide subtle
reasons for the stability of two-dimensional crystals(13-15).

摘要: Carbon nanotubes are graphene sheets rolled-up into
cylinders,with diameters as small as one nanometer. Extensive work carried out
worldwide in recent years has revealed the intriguing electrical and mechanical
properties of these novel molecular scale wires. It is now well established that
carbon nanotubes are ideal model systems for studying the physics in
one-dimensional solids and have significant potential as building blocks for
various practical nanoscale devices. Nanotubes have been shown to be useful for
miniaturized electronic, mechanical, electromechanical, chemical and scanning
probe devices and materials for macroscopic composites. Progress in nanotube
growth has facilitated the fundamental study and applications of nanotubes.
Gaining control over challenging nanotube growth issues is critical to the
future advancement of nanotube science and technology, and is being actively
pursued by researchers. (C) 2001 Elsevier Science B.V. All rights
reserved.

摘要: The potential energies of interaction between two
parallel, infinitely long carbon nanotubes of the same diameter, and between
C-60 and a nanotube in various arrangements, were computed by assuming a
continuous distribution of atoms on the tube and ball surfaces and using a
Lennard-Jones (LJ) carbon-carbon potential. The constants in the LJ potential
are different for graphene-graphene and C-60-C-60 interactions. From these, the
constants for tube-C-60 interactions were estimated using averaging rules from
the theory of dispersion forces. For tubes in ropes, the cohesive energy per
unit length, the compressibility, and the equilibrium separation distance were
computed as a function of tube radius. For a C-60 molecule interacting with
tubes, the binding energy inside a tube was much higher than on a tube or at the
tube mouth. Within a tube, the binding energy was highest at a spherically
capped end. The potential energies for tubes of all radii, as well as for
interactions between C-60 molecules, for a C-60 molecule outside of a nanotube,
between a C-60 molecule and a graphene sheet, and between graphene sheets, all
fell on the same curve when plotted in terms of certain reduced parameters.
Because of this, all the potentials can be represented by a simple analytic
form, thereby greatly simplifying all computations of van der Waals interactions
in graphitic systems. Binding-energy results were all consistent with the
recently proposed mechanism of peapod formation based on transmission electron
microscopy experiments.

摘要: Graphene sheets offer extraordinary electronic, thermal
and mechanical properties and are expected to find a variety of applications. A
prerequisite for exploiting most proposed applications for graphene is the
availability of processable graphene sheets in large quantities. The direct
dispersion of hydrophobic graphite or graphene sheets in water without the
assistance of dispersing agents has generally been considered to be an
insurmountable challenge. Here we report that chemically converted graphene
sheets obtained from graphite can readily form. stable aqueous colloids through
electrostatic stabilization. This discovery has enabled us to develop a facile
approach to large-scale production of aqueous graphene dispersions without the
need for polymeric or surfactant stabilizers. Our findings make it possible to
process graphene materials using low-cost solution processing techniques,
opening up enormous opportunities to use this unique carbon nanostructure for
many technological applications.

摘要: We derive an effective two-dimensional Hamiltonian to
describe the low-energy electronic excitations of a graphite bilayer, which
correspond to chiral quasiparticles with a parabolic dispersion exhibiting Berry
phase 2 pi. Its high-magnetic-field Landau-level spectrum consists of almost
equidistant groups of fourfold degenerate states at finite energy and eight
zero-energy states. This can be translated into the Hall conductivity dependence
on carrier density, sigma(xy)(N), which exhibits plateaus at integer values of
4e(2)/h and has a double 8e(2)/h step between the hole and electron gases across
zero density, in contrast to (4n+2)e(2)/h sequencing in a monolayer.

摘要: The synthesis of carbon nanotubes with predefined
structure and functionality plays a central role in the field of
nanotechnology(1,2), whereas the inhibition of carbon growth is needed to
prevent a breakdown of industrial catalysts for hydrogen and synthesis gas
production(3). The growth of carbon nanotubes and nanofibres has therefore been
widely studied(4-10). Recent advances in in situ techniques now open up the
possibility of studying gas - solid interactions at the atomic level(11-12).
Here we present time-resolved, high-resolution in situ transmission electron
microscope observations of the formation of carbon nanofibres from methane
decomposition over supported nickel nanocrystals. Carbon nanofibres are observed
to develop through a reaction-induced reshaping of the nickel nanocrystals.
Specifically, the nucleation and growth of graphene layers are found to be
assisted by a dynamic formation and restructuring of mono-atomic step edges at
the nickel surface. Density-functional theory calculations indicate that the
observations are consistent with a growth mechanism involving surface diffusion
of carbon and nickel atoms. The finding that metallic step edges act as
spatio-temporal dynamic growth sites may be important for understanding other
types of catalytic reactions and nanomaterial syntheses.

ISSN: 0028-0836

DOI: 10.1038/nature02278

显示 42 条，共 50 条

作者: Kane, CL; Mele, EJ

标题: Quantum spin Hall effect in graphene

来源出版物: PHYSICAL REVIEW LETTERS, 95 (22): Art. No. 226801 NOV
25 2005

摘要: We study the effects of spin orbit interactions on the low
energy electronic structure of a single plane of graphene. We find that in an
experimentally accessible low temperature regime the symmetry allowed spin orbit
potential converts graphene from an ideal two-dimensional semimetallic state to
a quantum spin Hall insulator. This novel electronic state of matter is gapped
in the bulk and supports the transport of spin and charge in gapless edge states
that propagate at the sample boundaries. The edge states are nonchiral, but they
are insensitive to disorder because their directionality is correlated with
spin. The spin and charge conductances in these edge states are calculated and
the effects of temperature, chemical potential, Rashba coupling, disorder, and
symmetry breaking fields are discussed.

摘要: Problems associated with large- scale pattern growth of
graphene constitute one of the main obstacles to using this material in device
applications(1). Recently, macroscopic- scale graphene films were prepared by
two- dimensional assembly of graphene sheets chemically derived from graphite
crystals and graphene oxides(2,3). However, the sheet resistance of these films
was found to be much larger than theoretically expected values. Here we report
the direct synthesis of large- scale graphene films using chemical vapour
deposition on thin nickel layers, and present two different methods of
patterning the films and transferring them to arbitrary substrates. The
transferred graphene films show very low sheet resistance of similar to 280
Omega per square, with 80 per cent optical transparency. At low temperatures,
the monolayers transferred to silicon dioxide substrates show electron mobility
greater than 3,700 cm(2) V-1 s(-1) and exhibit the half- integer quantum Hall
effect(4,5), implying that the quality of graphene grown by chemical vapour
deposition is as high as mechanically cleaved graphene(6). Employing the
outstanding mechanical properties of graphene(7), we also demonstrate the
macroscopic use of these highly conducting and transparent electrodes in
flexible, stretchable, foldable electronics(8,9).